The Effect of Prior Cathodic Polarization on the Initiation of Pitting on Aluminum

Prior cathodic polarization was found to increase pit densities on aluminum by a factor of 100 during the first 20 ms of anodic polarization above the pit initiation potential, in at 65°C. Enhancements of the average pit growth current densities were also observed. Immersion of aluminum in solutions of , or followed by , before cathodic polarization, was also necessary to obtain cathodic enhancement of pitting. The total pit volume at 20 ms was approximately the faradaic equivalent volume of the cathodic charge, calculated assuming three cathodic electrons resulted in the removal of one Al atom during anodic polarization. This result suggests that the cathodic reaction may produce a species which participates in the initial stages of anodic dissolution.